The present invention relates to performance measuring equipment for sailboats, and more particularly to improved means for determining leeway angle and vessel speed.
In the thousands of years that man has been sailing, the only sure way of measuring sailing performance has occurred when one vessel tried to escape from another. The captains of both vessels would do everything possible to exploit the full potential of their ships in an attempt to either evade or capture the other. This method of evaluating sailboat performance is still used today. While it is only a measure of relative performance, the information which is gleaned regarding sail settings can be recorded for use in subsequent, similar situations.
The above-described method is of little use in determining absolute performance, however. The absolute performance of a sailboat may be defined as its velocity related only to true wind velocity. Herein it should be noted that the term "velocity" denotes a vector or quantity having both magnitude and direction.
While other parameters affect boat performance, most of them can be related to true wind velocity and other known values, if desired. Absolute performance can be determined on board a sailboat only if three vectors are known. These are (a) apparent wind velocity; (b) boat velocity; and (c) current velocity.
Of the foregoing factors, current velocity is usually not measured on baord a boat or ship. Test runs of the vessel are typically made in an area where currents are minimal, or of known velocity.
Apparent wind velocity is measured in relation to the longitudinal center line of the boat. Boat speed is measured (usually inaccurately due to the hull curves and heel angle) parallel to the longitudinal center line of the boat. According to prior art techniques, the accurate measurement of boat velocity required the use of expensive, elaborate equipment which, when used, was done so only on large expansive vessels.
In the past many efforts have been made to provide means for indicating the leeway of a vessel. In modern times sophisticated systems have been devised for accurate navigation; however, such systems are commonly too complex, and hence too expensive, for use in small privately owned boats. Further, such systems are ordinarily comprised by permanent installations and cannot easily be placed on a vessel to gather data for properly trimming the vessel.
Such devices as are now known, and adaptable for use in small vessels, ordinarily include a vane journaled upon a generally vertically-extending shaft. The shaft is conventionally journaled within a tube or other support fixed to the hull of the vessel. In some instances the shaft of the vane extends upwardly through the vessel, the leeway-indicating vane lying below the vessel in the region of the keel so that leeway of the vessel will cause rotation of the vane-carrying shaft. This results in the production of an indication at the bridge of a ship, such as the motion of a pointer or the like. For sailing craft, which commonly exhibit substantial heel, a significant error is introduced in such leeway indicating apparatus due to the heel of the craft. In particular, as the heel increases the deflection of the vane due to leeway decreases so that the further heeled a vessel is, the greater the error in indicated leeway. This is particularly disadvantageous inasmuch as sailing craft are conventionally heeled over furthest when the leeway is at a maximum. Moreover, the present inventor has found that a substantial error occurs whether a leeway indicator is constrained to heel with the vessel to which it is mounted or gimballed and allowed to ride free in the water.
Accordingly, it will be understood that it would be highly desirable to provide a compact leeway measuring system for use with small craft, and which overcomes the deficiencies inherent in prior art leeway measuring systems and which provides a more accurate indication of leeway.
It is therefore an object of the present invention to provide an improved leeway indicator.
Another object is to provide a leeway indicator which indicates true leeway despite the heel of the vessel to which it is mounted.
Still another object is to provide a leeway indicating system which is compact enough to be temporarily attached to small vessels for obtaining information regarding their operation.
Yet another object is to provide an improved sensing apparatus for developing speed and leeway data to assist the trimming and navigation of a sailing craft.
Yet another object is to provide a leeway measuring system including meals for maintaining a leeway vane in a substantially vertical orientation.